Ultracold measurements reveal shape of the electron

WHAT shape is an electron? The standard model of particle physics predicts that electrons are egg-shaped, but that the amount of distortion from a perfect sphere is so tiny that no existing experiment could possibly detect it. However, a rival theory called supersymmetry predicts that this egg-shaped distortion should be large enough to be detectable.

Jony Hudson and colleagues at Imperial College London set out to crack the problem. They used ultracold molecules of ytterbium fluoride in which the centres of positive and negative charge differ, creating a dipole. The shape of this dipole reflects the asymmetry of the electron shape, and the team measured this by placing the molecules in an electric and a magnetic field and observing how they spin as the fields are changed. Variations in the rate of spin reveal any asymmetry. Their experiment measured the shape to within a few parts in 1018 but as far as they could tell, rather than being oval, the electron is spherical (Nature, DOI: 10.1038/nature10104).

The result is a challenge to supersymmetry: while the standard model suggests the electron is egg-shaped by only one part in 1028, supersymmetry sets the range at between one part in 1014 and one part in 1019.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.